1. Field of the Invention
The invention herein relates to medical administration of liquids such as intravenous fluids and transfused blood. More particularly it relates to methods of maintaining a desired temperature of such fluids.
2. Description of the Prior Art
In many medical procedures and situations, it is necessary to administer fluids or liquids of one type or another to a patient. Typically a patient will be given one or more types of liquid medication or hydrating liquids through intravenous administration. Similarly, patients are often provided with transfused blood intravenously. Typical of the types of medical procedures or situations in which fluids are administered include during surgery, in treatment of cardiac arrest, in nurseries, during administration of blood from blood banks, to burn patients and during post-operative recovery.
It is well known that such liquids or fluids should not be at low temperatures when administered to the patients, since the temperature differential between the fluid's temperature and the patient's body temperature can have serious adverse effects upon the patient who is already in a weakened condition. For instance, when chilled a patient's circulatory system has less capacity to carry oxygen. The problem of chilling from cold fluids is particularly acute for patients during surgery, when a patient's system is already subject to the trauma of surgery and is also suppressed by the anesthetic, or during treatment for cardiac arrest. See, e.g., Bowen, J. Amer. Assoc. Nurse Anesths., 60, 4, 369-373 (1992); Bostek, J. Amer. Assoc. Nurse Anesths., 60, 6, 561-566 (1992); and Anon., Convention Reporter, 22, 2, 9 (Dec. 1992) [Meeting of Amer. Society of Anesthesiologists (Oct. 1992)].
Unfortunately, however, it is often difficult to deliver fluid to the patient at the appropriate temperature. Many fluids are held in refrigerated storage until just prior to administration to the patient. In addition, it is common practice for operating rooms and recovery rooms to be vigorously air conditioned or to use laminar air flow, both of which keep the ambient temperature quite low. While there are sound medical reasons for this practice, including the comfort of the surgical team during lengthy surgical procedures and inhibition of infection in the patient, it means that the fluids on hand in the operating room or recovery room will remain at lowered temperatures.
Since it has been recognized that hypothermia of surgical patients is a serious problem, and that use of chilled intravenous or transfused fluids will aggravate that condition and cause further cooling of internal organs, there have been numerous attempts in the past to provide techniques and equipment for heating such fluids prior to administration to the patient. The Bostek and Bowen articles mentioned above describe typical examples. Overall, these various devices have not proved uniformly successful. Stand-alone continuous electric heaters through which the fluids are passed tend to be cumbersome and must be positioned close to the patient, and are thus frequently in the way of the surgical team in what is already normally a very crowded area surrounding the operating table. They also require electrical power cords, and such cords interfere with the surgical team's movements and can be dangerous. In addition, they are costly to purchase and operate. Their use is, therefore, frequently avoided.
Alternatively, there have been efforts to use small tube-like devices which can be preheated and through which the fluid is flowed prior to administration to the patient. Such devices have had shortcomings. Being small, they rapidly cool and after a short time no longer heat the fluid effectively. Further, such devices have been difficult and time consuming to disengage from the fluid flow lines. The result has been that after an initial period of adequate heating, the fluid subsequently administered to the patient is once again in a chilled condition, since the surgical team members do not have the time to engage in lengthy disassembly, reheating and replacement of these devices.
Since the problem of hypothermia in patients and the aggravating effects of administration of chilled fluids is an on-going problem, it would therefore be advantageous to have a simple method for providing heat to these fluids, using a device of a sufficiently simple design that each unit could be quickly and easily replaced with another heated unit when the heating effect of the first significantly diminished. The fluids administered to the patients would therefore be kept substantially uniformly at the desirable administration temperature during the entire surgical procedure.